3,3′-Dipyridyl BINOL ligands.: Synthesis and application in enantioselective addition of Et2Zn to aldehydes

[GRAPHICS] 3,3'-Di(2-pyridyl) BINOLs (4), prepared in three steps from commercial substances by a combined directed ortho metalation-Negishi cross-coupling protocol, constitute new members of the BINOL ligand family. They are among the most selective, general ligands, providing equal or greater stereoselectivities in the Et2Zn addition to benzaldehydes and cinnamalclehydes (Table 3) than any single BINOL ligand reported to date.